I partially agree, SQL databases are typically used if 1 write event per 10 or more read events happens... I don't want flame...
But I agree with dokkeldepper too. Though I have no real experience with MySQL, the principles are universal: When you need quick search (which is really possible, your search query is simple), you should not write nothing into the db in this transaction, only read. I guess that your caching system is the bottleneck, imho. And I think you should try to realize search query without caching, directly from smartly indexed table(s), and, potentially, tune this query... But I have not any advice, how to establish the indexes on MySQL - I don't know how to realize index scan finding free rooms in MySQL efficiently.
Update: added 'partially' and the second paragraph :)

In reply to Re^5: OT: Scalable web application architecture by pajout
in thread OT: Scalable web application architecture by badaiaqrandista

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